The present invention relates to methods and devices for electrical stimulation of biological functions to assist in the treatment of certain abnormal biological conditions.
Human cells contain a bioelectrical potential across the cell membrane, thought to be generated by the differing concentrations of sodium and potassium ions inside and outside the cell. Under equilibrium conditions the electrical currents caused by the movement of sodium and potassium ions through the semipermeable cell membrane are equal, resulting in a zero net current flow and a resting potential difference of approximately -90 millivolts (mV). When the cell is electrically stimulated either by a nerve signal or by an external stimulus, the cell passes through a "cell action potential cycle." The sodium ionic current into the cell increases until the cell's internal voltage reaches a threshold level of approximately -60 mV, at which point the cell potential increases without further stimulation to a peak of approximately +20 mV. The cell is then referred to as being in a "depolarized" state. The cell then "repolarizes" to a -90 mV state as the ionic concentrations return to equilibrium. This cell activity has been referred to as the "sodium-potassium pump," as generally described for example at pages 7- 21 of Biophysical Measurements, by Peter Strong, published by Tektronix, Inc. (1971).
The sodium-potassium pump action is thought to be important in the maintenance of physical health, and is normally provided by ordinary nerve signals in healthy tissue. When ordinary nerve signals are interrupted, however, as for example by trauma or by calcification in the case of arthritis, it is believed that this cell action may be reduced or impaired or may cease altogether. Application of external voltage pulses is thought to assist in reestablishing cell action within the affected area and thus promote healing.
Devices for applying electrical stimulation to the human body are well known in the art, but they have generally utilized alternating electrical fields because of the possibility of undesired electrolysis at the point of contact between the tissue and the electrodes. Further, such devices generally have not utilized magnetic fields to aid the penetration of the electric current into the tissues being treated. As a result it is believed that the electric current failed to penetrate deeply into the tissue, but rather traveled along the skin from one electrode to the other. Healing of deep tissue therefore was not significantly aided. Current levels sufficient to penetrate deep tissue were often hazardous to the patient.
In U.S. Pat. No. 3,915,151 (Kraus), there was disclosed a device for treating injured body tissue by passing alternating electric and magnetic fields through the tissue at the same time, and two fields having approximately the same energy content and being approximately ninety degrees out of phase. However, there was no direct connection between the electrodes and the patient, and the magnetic field was of relatively low intensity. Thus optimum results could not be achieved. In addition, the electric field was applied at right angles to the body's natural current flow, hindering maximum efficiency of the device. The lines of magnetic force, on the other hand, ran approximately parallel to the skin surface, and thus provided no aid in penetration of the current into the deep tissues.
United States Patents disclosing only the application of electrical stimulation to the body include Brouner U.S. Pat. Nos. 3,055,372, Jonsson 3,476,117 and Hagfors 3,645,267. Stimulation by electrical current is provided by devices disclosed in Bowers et al U.S. Pat. Nos. 3,726,285; Holcomb et al 3,773,051; Mauer 3,888,261; Weiss 3,924,641; Nozhinkov et al 3,989,051; and Geerling 4,019,519. Hallgren U.S. Pat. No. 3,841,305 discloses a device for nerve stimulation by induction. Temporary relief of arthritic pain is claimed to be provided by devices disclosed in Paul, Jr. U.S. Pat. Nos. 3,881,494, and Liss et al 3,902,502. Devices for electrotherapy by tissue stimulation are disclosed in Nawracaj U.S. Pat. Nos. 3,794,022; Horn 3,918,459; and Ellis 4,019,510. Hagfors et al 3,911,930 discloses a device for electrotherapy by application of generally rectangular or square wave pulses to the body. Manning U.S. Pat. No. 3,893,462 discloses devices for inductive stimulation of tissue as well as stimulation by direct application of current.
Another prior device with which applicant is familiar involved an applicator device containing a pair of spaced electrodes and an electromagnet therebetween. The electrodes were supplied with a relatively minimal level of direct current, within the range of 50-100 microamperes and usually 20-25 microamperes, and a voltage up to 6 volts dc. The current was reversed rapidly in polarity in an attempt to minimize adverse effect on tissue and bone structure. The electromagnet was electrically powered from a rotating potentiometer which supplied approximately 0 to 45 volts dc to the electromagnet to obtain a sweeping effect of the current into the tissue. It was subsequently determined that such device was not satisfactory because of the voltage and current parameters and because of the substantially adverse effect of the use of current reversal which apparently prevented proper tissue stimulation.